System and methods for identifying tissue and vessels

ABSTRACT

A surgical system and corresponding methods for identifying tissue or vessels and assessing their conditions includes a probing signal source for applying a probing signal to the tissue and a response signal monitor for monitoring a response signal that varies according to the level of blood circulation in the tissue or vessels. The response signal monitor monitors the response signal over an interval equal to or longer than air interval between two successive cardiac contractions. The surgical system includes a microprocessor that analyzes the amplitude and/or phase of the response signal to determine the level of blood circulation in the tissue or in different portions of the tissue, and determines a tissue parameter based upon the level of blood circulation. The surgical system may monitor a cardiac signal related to cardiac contractions and correlate the response signal and the cardiac signal to determine a level of blood circulation in the tissue.

BACKGROUND 1. Technical Field

The present disclosure relates to in vivo systems and methods ofidentifying tissue parameters (e.g., tissue type) and assessing theconditions of the tissue during a surgical procedure, More specifically,the present disclosure relates to systems and methods for measuring therelative level of blood circulation in tissue with an energy-basedsurgical instrument for vessel sealing.

2. Background of Related Art

Correctly identifying tissue parameters including tissue type isimportant for any surgical operation. But it is especially importantduring laparoscopic operations when a surgeon can only view tissuethrough a camera. A camera, however, may provide a surgeon with alimited view of the tissue. As a result, several ex vivo and in vivomethods have been proposed to measure different characteristics oftissue in order to identify and assess the tissue.

Publication number US 2008/0200843 describes a method and apparatus formeasuring human tissue properties in vivo. The method is based onsensing the mechanical response of tissue. The method includes applyinga predetermined force to the surface of a patient with a probe andmeasuring the displacement of the probe as a function of applied force,Tissue properties are then determined based on the result of measuringthe displacement of the probe.

Publication number US 2008/0154145 describes a method and apparatus fordetermining characteristics of biological tissues. Tissuecharacteristics are determined by introducing a sound wave into thetissue and recording the response of the tissue to the sound wave.

Publication number US 2009/0124902 describes a method for classifyingtissue from the lumbar region using a combination of ultrasonic andoptical measurements.

In publication number US 2007/0276286, a miniature electrode array isused to stimulate tissue and to measure a tissue response in order toprovide tissue diagnosis and spatial tissue mapping.

Publication number US 2005/0283091 describes a method and apparatus fordetermining the conditions of biological tissue. The method includesexciting tissue with electrical signals at different frequencies andanalyzing the cross-correlation of response signals with delayedexcitation signals, Cross-correlation products are then auto-correlated.Cross-correlation products correspond to tissue conditions andauto-correlation products correspond to changes in the tissueconditions.

Publication number US 2003/0060696 discloses an apparatus forrecognizing tissue type using multiple measurement techniques. Forexample, electrical signals are applied to a tissue via electrodes tomeasure impedance magnitude and phase at a plurality of frequencies. Thephase information at the plurality of frequencies is compared with thephase information of known tissue types to identify the tissue type.

Publication number US 2002/0077627 describes a method for detecting andtreating tumors using localized impedance measurements. The methodincludes providing an impedance measurement apparatus having a pluralityof resilient members deployable to sample tissue impedance through aplurality of conductive pathways, information from the impedancemeasurements is then used to determine the condition of the tissue.

Publication number US 2009/0253193 describes a device for characterizingtissue ex vivo. The device includes a set of independent electrodes thatscan the tissue by moving a voltage gradient across the tissue surfaceand acquiring impedance spectrographs that may be mapped to an image.

U.S. Pat. No. 5,769,791 describes a tool for nondestructiveinterrogation of the tissue including a light source emitter anddetector, which may be mounted directly on the surgical tool in a tissuecontacting surface or mounted remotely and guided to the surgical fieldwith fiber optic cables.

Publication number US 2009/0054908 describes a system having a surgicalinstrument with a sensor for generating a signal indicative of aproperty of a patient's tissue. The signal is converted into a currentdataset and stored. A processor compares the current dataset with otherpreviously stored datasets and uses the comparison to assess a physicalcondition of the tissue and/or to guide a procedure being performed onthe tissue.

Although existing methods can provide various measurements of tissueparameters, these methods may be difficult to implement because of theircomplexity and may provide inaccurate measurements.

SUMMARY

The systems and methods according to embodiments of the presentdisclosure provide accurate information about tissue parameters andconditions. These systems and methods also provide a relatively quickand simple way to identify tissue parameters and conditions duringlaparoscopic procedures without requiring the introduction of additionalinstruments or tools into a patient's body.

According to one aspect, the present disclosure features a method ofdetermining a tissue parameter. The method includes applying a probingsignal to tissue, monitoring a response signal over an interval longerthan an interval between two successive cardiac contractions,determining the amplitude of the response signal, determining the levelof blood circulation in the tissue based upon the amplitude of theresponse signal, and determining a tissue parameter based upon the levelof blood circulation. The probing signal is configured to interact withthe tissue in a predetermined way.

In some embodiments, the tissue parameter is a tissue type, such asconnective tissue, muscle tissue, nervous tissue, or epithelial tissue.In other embodiments, the tissue type includes a vessel type, such as abile vessel, a lymph vessel, a blood vessel, an artery, an arteriole, acapillary, a venule, or a vein. In yet other embodiments, the tissueparameter is the tissue condition, such as whether the tissue isdamaged.

In some embodiments, determining the amplitude of the response signalincludes determining the amplitude of the response signal at thefrequency of the cardiac contractions or at the harmonics of thefrequency of the cardiac contractions. In other embodiments, the methodof identifying tissue parameters may include applying the probing signalto different portions of the tissue, determining the amplitude of theresulting response signals to determine the level of blood circulationin the different portions of the tissue, and determining the tissueparameter based on the level of blood circulation in the differentportions of the tissue.

The probing signal may be an acoustical signal, an optical signal, or anRF signal: In the case where the probing signal is an RF signal,monitoring the response signal includes monitoring the response signalat a frequency within a range from 10 kHz to 10 MHz. In someembodiments, monitoring the response signal includes monitoring theresponse signal with an energy-based tissue sealing instrument. In otherembodiments, determining the amplitude of the response signal includesdetermining the amplitude and phase of the response signal.

In another aspect, the present disclosure features another method ofdetermining a tissue parameter. The method includes applying a probingsignal to tissue, monitoring a response signal that has interacted withthe tissue over an interval longer than an interval between twosuccessive cardiac contractions, monitoring a cardiac signal related tocardiac contractions, correlating the response signal and the cardiacsignal, determining a level of blood circulation in the tissue basedupon the result of correlating the response signal and the cardiacsignal, and determining a parameter of the tissue based upon the resultof determining the level of blood circulation in the tissue. In someembodiments, the parameter of the tissue is a type of the tissue. Thetype of the tissue may be connective tissue, muscle tissue, nervoustissue, or epithelial tissue.

In yet another aspect, the present disclosure features a system fordetermining a tissue parameter. The system includes a probing signalsource configured to apply a probing signal to tissue, a response signalmonitor configured to monitor a response signal over an interval longerthan an interval between two successive cardiac contractions, and aprocessor configured to analyze the amplitude of the response signal todetermine a level of blood circulation in the tissue. The processor isfurther configured to determine a tissue parameter based on the level ofblood circulation. In some embodiments, the system further includes anelectrosurgical energy source configured to apply electrosurgical energyto tissue during an electrosurgical procedure. In these embodiments, theprobing signal source is the same source as the electrosurgical energysource.

BRIEF DESCRIPTION OF THE DRAWINGS

The systems and methods of in vivo assessment of tissues and vesselswill now be described with reference to the accompanying drawings, inwhich:

FIG. 1 is a block diagram of a system for recognizing tissue and vesselsbased on blood circulation according to embodiments of the presentdisclosure;

FIGS. 2A and 2B are cross-sectional side views of a portion of theinstrument of FIG. 1 having jaw members for grasping tissue and bloodvessels according to embodiments of the present disclosure;

FIG. 3 is a graphical diagram showing impedance variations induced byblood circulation and measured with an RF-based tissue sealing deviceaccording to embodiments of the present disclosure;

FIG. 4 is a graphical diagram showing the frequency spectrum of theimpedance variations illustrated in FIG. 3; and

FIGS. 5 and 6 are flow diagrams of methods for recognizing parameters oftissue and vessels according to embodiments of the present disclosure.

DETAILED DESCRIPTION

Different types of human and animal tissues have different densities ofblood vessels (i.e., the number of blood vessels per unit area or volumeof tissue) and experience different levels of blood circulation (i.e.,the amount of blood flow per unit volume of tissue). These parameterscan be used to identify different types of tissues during a surgicalprocedure. For example. When the tissue structure changes as a result ofdamage to the tissue, the blood circulation usually changes as well.This phenomenon allows one to distinguish between damaged and normalportions of tissue by comparing corresponding levels of bloodcirculation. As another example, when tumors form and grow in normaltissue, the density of blood vessels in the tissue increases becausethese tumors depend on the formation of new blood vessels for theirgrowth. Thus, by measuring the density of blood vessels or the level ofblood circulation in tissue, one can distinguish between a tumor andnormal tissue.

For some surgical procedures, such as electrosurgical procedures, thesurgeon may need to distinguish between blood vessels and other types ofvessels, e.g., bile ducts. For blood vessels, the surgeon may need tocheek for blood clots or other structural changes in the blood vessels.For vessel sealing procedures, the surgeon may need to confirm that thevessel has been properly sealed before it is cut. In all of theseprocedures, the tissue or vessel can be examined to assess bloodcirculation conditions. Information regarding blood circulationconditions may inform a surgeon regarding the type of the tissue orvessel and/or the condition of the tissue or vessel.

FIG. 1 is a block diagram of an energy-based tissue-sealing system 100for recognizing tissue or vessels based upon blood circulation in thetissue or vessels according to embodiments of the present disclosure.The system 100 (and the methods described below) may use any type ofenergy to seal tissue including mechanical energy, acoustical energy,thermal energy, electric energy, or electromagnetic energy (e.g.,optical energy or radio frequency (RF) energy).

The system 100 includes a power supply 122, an energy output stage 124,and an instrument 126. The power supply 122 supplies power to the energyoutput stage 124, which generates energy and provides the energy to theinstrument 126. The instrument 126, in turn, applies the generatedenergy to the tissue 101, which includes at least one vessel 102. For anRF-based tissue-sealing system, the energy output stage 124 generates RFenergy and the instrument 126 applies the RF energy to the tissue 101through at least one contact to seal the tissue 101.

The system 100 also includes a sensor 112, a microprocessor 114, a userinterface 116, and a display 118. The sensor 112 senses variousparameters and/or properties of tissue 101 at the operating site andtransmits sensor signals representing the sensed parameters orproperties of the tissue 101 to the microprocessor 114. Themicroprocessor 114 processes the sensor signals and generates controlsignals based on the processed sensor signals to control the powersupply 122 and/or the energy output stage 124. For example, themicroprocessor 114 may regulate the voltage or current output from thepower supply 122 or the energy output stage 124 based on the processedsensor signals.

The sensor 112 is configured to measure various electrical orelectromechanical conditions at the operating site such as tissueimpedance, changes in tissue impedance, tissue temperature, changes intissue temperature, leakage current, applied voltage, and appliedcurrent. The sensor 112 continuously measures one or more of theseconditions so that the microprocessor 114 can continually adjust theenergy output from the power supply 122 and/or the energy output stage124 during a sealing procedure. For example, in an RF-based vesselsealing instrument, the sensor 112 may measure tissue impedance and themicroprocessor 114 may adjust the voltage generated by the energy outputstage 124.

The user interface 116 is coupled to the microprocessor 114 allowing auser to control various parameters of the energy applied to the tissue101 during a surgical procedure. For example, the user interface 116 mayallow a user to manually set, regulate and/or control one or moreparameters of the energy delivered to the tissue, such as voltage,current, power, frequency, and/or pulse parameters, e.g., pulse width,duty cycle, crest factor, and/or repetition rate.

The microprocessor 114 can execute software instructions for processingdata received from the user interface 116 and for outputting controlsignals to the power supply 122 and/or the energy output stage 124. Thesoftware instructions are stored in an internal memory of themicroprocessor 114, an internal or external memory bank accessible bythe microprocessor 114 and/or an external memory, e.g., an external harddrive, floppy diskette, or CD-ROM. Control signals generated by themicroprocessor 114 may be converted to analog signals by adigital-to-analog converter (DAC) (not shown) before being applied tothe power supply 122 and/or energy output stage 124.

For some embodiments of an RF-based tissue-sealing system, the powersupply 122 is a high-voltage DC power supply that produces RF current.In these embodiments, the microprocessor 114 transmits control signalsto the power supply to control the magnitudes of the RF voltage andcurrent output from the power supply 122. The energy output stage 124receives the RF current and generates one or more pulses of RF energy.The microprocessor 114 generates control signals to regulate the pulseparameters of the RF energy, such as pulse width, duty cycle, crestfactor, and repetition rate. In other embodiments, the power supply 122is art AC power supply, and the energy output stage 124 may vary thewaveform of the AC signal generated by the power supply 122 to achieve adesired waveform.

As described above, the energy-based tissue-sealing system 100 includesa user interface 116, The user interface 116 includes an input device,such as a keyboard or touch screen, through which a user enters data andcommands. The data may include the type of instrument, the type ofprocedure, and/or the type of tissue. The commands may include targeteffective voltage, current, or power level, or other commands forcontrolling parameters of the energy that is delivered from the energyoutput stage 124 to the instrument 126.

The system 100 also includes a probing signal source 108 and a responsesignal monitor 105. The probing signal source 108 applies a probingsignal 109 to the tissue 101 and the response signal monitor 105 sensesa response signal 104. The response signal 104 is the probing signal 109that has been transmitted and/or scattered by the tissue 101 and vessel102. The probing signal 109 and the response signal 104 may beacoustical signals, optical signals, RF signals, or any combination ofthese signals. In some embodiments, the probing signal source 108 is theenergy output stage 124, The energy output stage 124 may generate aprobing signal 109 that is the same as the electrosurgical energyapplied to the tissue 101 to perform an electrosurgical procedure (e.g.,vessel sealing). Alternatively, the energy output stage 124 may generatea probing signal 109 that has parameters that are different from theparameters of the electrosurgical energy applied to the tissue 101.

The response signal monitor 105 generates a sensor signal or sensor databased on the response signal 104 and transmits the sensor signal orsensor data to the microprocessor 114. The microprocessor 114 processesthe sensor signal or sensor data to determine the level of bloodcirculation in the tissue 101 or vessel 102. For example, themicroprocessor 114 may determine the level of blood circulation based onthe magnitude of the sensor signal or the response signal 104.

The response signal 104 may provide information about the tissue type.For example, the response signal 104 may identify the tissue asconnective tissue, muscle tissue, nervous tissue, epithelial tissue, orany combination of these tissue types. The response signal 104 may alsoidentify the vessel type within the tissue 101. The vessel types includebile vessels, lymph vessels, and blood vessels. The response signal 104may distinguish the type of blood vessel that resides in a given portionof tissue. The types of blood vessels include arteries, arterioles,venules, and veins. The response signal 104 may also be used to identifythe condition of the tissue, such as whether the tissue is damaged.

The system 100 may determine the level of blood circulation by sensingtissue parameters or properties that depend on the level of bloodcirculation during a period exceeding one cardiac cycle. In someembodiments, the system 100 may sample tissue parameters or propertiesfor multiple cardiac cycles to more accurately determine the level ofblood circulation. In other embodiments, a cardiac signal, which isrelated to heart contractions (e.g., an electrocardiographic signal),can be used to evaluate the correlation between the parameters of thesensor signal and the cardiac signal to more accurately assess the levelof blood circulation.

FIGS. 2A and 2B show portions of an embodiment of the energy-basedinstrument 126 of FIG. 1 having jaw members 203, 204 configured to graspand compress tissue 101 and vessels 102. The jaw members 203, 204include electrodes or contacts 205, 206 that are electrically coupled tothe energy output stage 124, The electrodes 205, 206 receive energy fromthe energy output stage 124 and apply it to the tissue 101 and vessels102 to seal the tissue 101 and vessels 102.

As described above, the energy-based instrument 126 is also configuredto evaluate blood circulation in a given volume of tissue 101. Toevaluate blood circulation, the given volume of tissue 101 is firstgrasped between the jaw members 203, 204 of the energy-based instrument126. The pressure that is applied to the tissue 101 by the jaw members203, 204 is selected to provide electrical contact between theelectrodes 205, 206 and the tissue 101. However, the amount of pressureapplied to the tissue 101 may be lower than the amount of pressure usedto compress the tissue 101 during tissue sealing. Then, a probing signal109 (e.g., an RF signal) is applied to the tissue 101 by the electrodes205, 206 and a response signal 104 (e.g., tissue impedance) is measuredduring one or more cardiac cycles.

During the cardiac cycles, the pressure of the blood flowing in theblood vessels 102 varies and, as a result, the relative amount of bloodin a given volume of tissue 101 also varies. For example, as shown inFIG. 2A, during a first portion of the cardiac cycle, the pressure ofthe blood flowing within the blood vessels 102 is at a low level and thevolume of blood within the given volume of tissue 101 is at a low level.On the other hand, as shown in FIG. 1B, during a second portion of thecardiac cycle, the pressure of the blood flowing within the bloodvessels 102 is at a high level and the volume of blood within the givenvolume of tissue 101 is at a high level. The volume of blood within thegiven volume of tissue 101 may be measured by measuring the impedance ofthe tissue 101. The impedance may be measured by applying the probingsignal 109 to the tissue 101 and sensing the response signal 104.

During a cardiac cycle, as the volume of blood in a given volume oftissue increases, a force is applied to the jaw members 203, 204 toincrease the distance between the jaw members 203, 204, In someembodiment, the system 100 includes a motion sensor configured to sensethe change in distance between the jaw members 203, 204, This distanceinformation may be used together with the response signal 104 toevaluate the level of blood circulation within a given volume of tissue101.

As described above, a probing signal 109 is applied to a vessel and aresponse signal 104 is measured over time to identify tissue 101 and/orvessels 102 or to determine parameters of the tissue 101 and/or thevessels 102. The response signal 104 may include the frequency andamplitude of an electrical impedance of the tissue 101. If the frequencyof the electrical impedance correlates to the frequency of cardiaccontractions, then the vessel 102 is identified as a blood vessel. Ifthe vessel is identified as a blood vessel, the amplitude of theelectrical impedance would indicate the level of blood circulation.

FIG. 3 is a graph showing experimentally-measured impedance of tissue302 versus time. The graph has a y-axis 311 that indicates the tissueimpedance in ohms and an x-axis 312 that indicates the time in seconds.As shown in FIG. 3, the measured impedance 302 continually variesaccording to the cardiac cycles where a cardiac cycle is the distancebetween the peaks of the measured impedance 302. In this case, themeasured impedance 302 has a peak-to-peak amplitude of approximately 0.1ohms and a period of approximately 0.8 seconds (which corresponds to aheart rate of 75 beats per minute). The measured impedance 302 variesaccording to the cardiac cycles because the volume of blood within agiven volume of tissue 101 varies according to the cardiac cycles. Inother words, the measured impedance 302 correlates with the volume ofblood within a given volume of tissue 101. Depending on the design ofthe instrument, it is also possible that an increase in blood pressurecan expand the grasped tissue and, as a result, the tissue volumebetween the jaw members changes. This effect may also contribute tovariations in measured impedance.

FIG. 4 is a graph showing the frequency spectrum ofexperimentally-measured impedance variations in tissue corresponding toFIG. 3. The graph has a y-axis 411 that indicates the spectral powerdensity of the experimentally-measured impedance variations in tissueand an x-axis 412 that indicates the frequency in Hertz. The graph showsmodulation variations related to the fundamental frequency of cardiaccontractions 402 and its harmonics 403, 404. In this case, thefundamental frequency of cardiac contractions 402 is approximately 1.25Hz, which corresponds to a cardiac cycle of approximately 0.8 seconds inFIG. 3. The measured impedance also includes variations related tobreathing 401 and the inter-modulation products between the variationsdue to heart contraction and the variations due to breathing.

FIG. 5 is a flow diagram of a process for identifying parameters oftissue and vessels according to embodiments of the present disclosure.After the process starts in step 501, a probing signal 109 is applied totissue in step 502. The probing signal 109 interacts with the tissue tocreate a response signal 104. In step 504, the response signal 104 ismonitored over an interval equal to or longer than an interval betweentwo successive cardiac contractions. The response signal may bemonitored at a frequency within a range between 10 kHz and 10 MHz using,e.g., an energy-based tissue sealing instrument.

Next, in step 506, the amplitude of the response signal 104 isdetermined. The amplitude of the response signal 104 may be determinedat a frequency of the cardiac contractions or at the harmonics of thefrequency of the cardiac contractions. Then, in step 508, the level ofblood circulation in the tissue is determined based on the amplitude ofthe response signal 104. In other embodiments, the amplitude and phaseof the response signal 104 are analyzed to determine the level of bloodcirculation in the tissue. Finally, before the process ends in step 511,a tissue parameter is determined in step 510 based on the level of bloodcirculation.

In some embodiments, the probing signal source 108 of FIG. 1 applies aprobing signal to different portions of the tissue. The response signalmonitor 105 then monitors parameters of the response signals and themicroprocessor 114 determines the level of blood circulation indifferent portions of the tissue based on the response signals. Themicroprocessor 114 may also determine parameters of the tissue based onthe level of blood circulation in different portions of the tissue.

FIG. 6 is a now diagram of a process for identifying parameters oftissues and vessels according to other embodiments of the presentdisclosure. As in FIG. 5, after the process starts in step 601, aprobing signal 109 is applied to tissue in step 602. The probing signal109 interacts with the tissue to create a response signal 104. In step604, the response signal 104 is monitored over an interval equal to orlonger than an interval between two successive cardiac contractions. Inaddition, a cardiac signal related to cardiac contractions is monitoredin step 606. In step 608, the response signal 104 and the cardiac signalare correlated. Then, in step 610, the level of blood circulation in thetissue is determined based upon the result of correlating the responsesignal 104 and the cardiac signal. Finally, before the process ends instep 613, a tissue parameter is determined in step 612 based upon theresult of determining the level of blood circulation in the tissue. Asdescribed above, the tissue parameter may include the tissue type, suchas connective tissue, muscle tissue, nervous tissue, or epithelialtissue.

Although the illustrative embodiments of the present disclosure havebeen described herein with reference to the accompanying drawings, it isto be understood that the disclosure is not limited to those preciseembodiments, and that various other changes and modifications may beeffected therein by one skilled in the art without departing from thescope or spirit of the disclosure.

1-14. (canceled)
 15. A method of determining a tissue parameter,comprising: applying a probing signal to tissue, the probing signalbeing configured to interact with the tissue; monitoring a responsesignal that has interacted with the tissue over an interval longer thanan interval between two successive cardiac contractions; monitoring acardiac signal related to cardiac contractions; correlating the responsesignal and the cardiac signal; determining a level of blood circulationin the tissue based upon the result of correlating the response signaland the cardiac signal; and determining a parameter of the tissue basedupon the result of determining the level of blood circulation in thetissue.
 16. The method of claim 15, wherein the parameter of the tissueis a type of the tissue.
 17. The method of claim 16, wherein the type ofthe tissue is selected from the group consisting of connective tissue,muscle tissue, nervous tissue, and epithelial tissue.
 18. A system fordetermining a tissue parameter, comprising: a probing signal sourceconfigured to apply a probing signal to tissue; a response signalmonitor configured to monitor a response signal over an interval longerthan an interval between two successive cardiac contractions; and aprocessor configured to analyze the amplitude of the response signal todetermine a level of blood circulation in the tissue, the processorfurther configured to determine a tissue parameter based on the level ofblood circulation.
 19. The system of claim 18, further comprising anelectrosurgical energy source configured to apply electrosurgical energyto tissue during an electrosurgical procedure, wherein the probingsignal source is the same source as the electrosurgical energy source.